Line versus Flux Statistics -- Considerations for the Low Redshift Lyman-alpha Forest

The flux/transmission power spectrum has become a popular statistical tool in studies of the high redshift ($z>2$) Lyman-alpha forest. At low redshifts, where the forest has thinned out into a series of well-isolated absorption lines, the motivation for flux statistics is less obvious. Here, we study the relative merits of flux versus line correlations, and derive a simple condition under which one is favored over the other on purely statistical grounds. Systematic errors probably play an important role in this discussion, and they are outlined as well.